Circuits for regulating a current

ABSTRACT

The current flow through a series leg, composed of the collector-emitter path of a transistor, of a load resistor connected to the collector, and of a substantially non-inductive resistor connected to the emitter, is regulated by a reference voltage provided between the free terminal of the latter resistor and the base of the transistor. The voltage can vary linearly with the operating voltage applied to the said free end, in dependence on temperature, or in dependence on some other factor, or can be constant. A diode can be conductively connected between the base and the reference voltage. The resistance of the load resistor is less than that of the substantially non-inductive resistor.

United States Patent Kraft [54] CIRCUITS FOR REGULATING A CURRENT [72]Inventor: Wolfgang Kraft, Bad Hersfeld, Germany [73] Assignee: SiemensAktiengesellschaft, Berlin and Munich, Germany [22] Filed: March 24,1971 [21] Appl. No.: 127,454

[30] Foreign Application Priority Data March 25, 1970 Germany ..P 20 14351.5

[52] US. Cl. ..307/297, 307/300, 323/22 T [51] Int. Cl ..G05f 1/40 [58]Field of Search ..307/297, 300; 330/22; 323/22 T [56] References CitedUNITED STATES PATENTS 3,359,433 12/1967 Thauland ..307/262 3,532,90910/1970 Buckley ..307/213 3,534,279 10/1970 Limberg ..330/22 1 Nov. 14,1972 3,250,922 5/ 1966 Parham ..307/297 3,518,458 6/1970 Camenzind..307/297 3,421,102 l/l969 Andrews ..307/297 Primary ExaminerJames W.Lawrence Assistant ExaminerHar01d A. Dixon Attorney-Michael S. Striker[57] ABSTRACT The current flow through a series leg, composed of thecollector-emitter path of a transistor, of a load resistor connected tothe collector, and of a substantially noninductive resistor connected tothe emitter, is regulated by a reference voltage provided between thefree terminal of the latter resistor and the base of the transistor. Thevoltage can vary linearly with the operating voltage applied to the saidfree end, in dependence on temperature, or in dependence on some otherfactor, or can be constant. A diode can be conductively connectedbetween the base and the reference voltage. The resistance of the loadresistor is less than that of the substantially non-inductive resistor.

14 China, 4 Drawing Figures PATENTED Nov 14 m2 IKZ INVhN'I UR WOLFGANG;KRAFT ATTURNEY' CIRCUITS FOR REGULATING A CURRENT BACKGROUND OF THEINVENTION The invention relates to a circuit for regulating theamplitude of current particularly of current pulses, ina series leg,composed of a load resistor, of the emittercollector path of atransistor, of a substantially non-inductive resistor, and of a sourceof voltage.

With known circuits of this kind, the current through the load resistoris switched by means of a transistor and of a transformer. Controlpulses are conducted to a first winding of the transformer, a secondwinding of the transformer being connected to the base and to theemitter of a transistor. In this known circuit, the ohmic resistance ofthe load current circuit is substantially greater than that of the loadresistor, so that the current is influenced virtually only by the ohmicresistance and not by the load resistor. Since the tolerance of theohmic resistance is a relatively small plus or minus 1 percent, theamplitude of the current pulse in the load current circuit can be heldlargely constant without requiring a special regulatory arrangement.This is particularly the case, when changes in the load current circuit,caused by temperature fluctuations, can be ignored.

This known circuit has the disadvantage, however, that a relativelylarge amount of power is used in the load current circuit, because thecurrent flow requires a relatively high voltage in view of thelargeohmic resistance. Further difficulties arise when temperaturefluctuations change the individual circuit parameters.

SUMMARY OF THE INVENTION An object of the invention is a circuit forregulating the amplitude of the current in a load current circuit,particularly current pulses, which circuit requires relatively littlepower and is largely stabilized against changes in circuit parameterscaused by temperature fluctuations or by changes in the values of thecircuit components.

A further object of the invention is a circuit of the preceding object,which circuit is suitable for operation over a temperature range of from-55C. to +125C.

Briefly, the invention consists of a first transistor, a series currentpath in which the control pulses are conducted, the series current pathincluding the emittercollector path of the first transistor andconnected in series with the emitter-collector path a load resistor anda substantially non-inductive resistor, the latter resistor beingsmaller in resistance than the load resistor, a. circuit junction, thebase of the first transistor being connected to this junction, a sourceof operating voltage having two terminals, the voltage differencebetween one terminal of this source and the circuit junctionconstituting a reference voltage, and controlled electronic switchingmeans connected between the base and a constant potential.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims.

The invention itself, however, both as to its construction and itsmethod of operation, together with additional objects and advantagesthereof, will be best understood from the following description ofspecific embodiments when read in connection with the accompanyingdrawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of thefirst embodiment of the invention, in which the reference voltage isindependent of the operating voltage;

FIG. 2 is a circuit diagram of a second embodiment, in which thereference voltage, obtained by means of a diode, is dependent on theoperating voltage; and

FIGS. 3 and 4 are graphs in which are plotted the change in current andvoltage at different points in the circuit of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIG. 1, thecircuit consists of first transistor 1 and additional transistor 2, oftwo substantially non-inductive resistors 4 (56 ohms) and 10 (1.2 ohms),of the load resistor 5 (5.1 ohms), and of the diode 6. A source 13 ofoperating voltage (5 volts) is connected between the terminal 7 and theground ter minal. The resistance of the resistor 10 is substantiallysmaller than that of the load resistor 5. In many cases, the ratiobetween the resistors 10 and 5 can be from 1:2 to 1:5 Resistors 5 and10, together with the collectoremitter path of transistor 1, form acurrent path for control current or voltage pulses. Fixed potentialmeans, here in form of a simple conductor connects the emitter oftransistor 2 to ground.

It will be assumed that the operating voltage is held constant within 2percent. Because of limitations in manufacture, and because of aging,the resistances of the resistors 10 and 5 and the resistance of theemittercollector path of the first transistor 1 are accurate only withincertain tolerances. The tolerance for the resistor 10 is i 1 percent.The tolerances for the emitter-follower path of transistor 1 and for theload resistor 5 are respectively 1 25 percent and 1+: 7 percent. Thecircuit described is intended for operation within a temperature range55C. to +C. It is also assumed that for changes in temperature over arange from -55C. to +125C. the resistor 10 changes plus or minus 1percent, the resistance of the emitter-collector path of transistor 1changes 1 10 percent, and the resistance of the load resistance 5changes i 5 percent.

The circuit shown in FIG. 1 regulates the amplitude of the current pulsei. In spite of the aforesaid tolerances and temperature-caused.resistance changes, the current pulse should be regulated as preciselyas possible, and variation should. not exceed 1 1 percent. By way ofexample, it may be required to regulate the current pulse i independentof the temperature. On the other hand, it may be required to regulatethe amplitude of the current pulse in dependence on the temperature orin dependence on some other factor.

If a positive pulse is applied to the terminal 9, the emitter-collectorpath of the additional transistor 2 becomes conductive, a currentthereby flowing through the resistor 4, the diode 6, and the base offirst transistor 1. Consequently, the emitter-collector path oftransistor 1 becomes conductive, and a current pulse i appears in theload current circuit. The amplitude of this current pulse depends on thereference voltage that exists between the terminal 7 and the circuitjunction 8 afforded by source of reference voltage 14. When thisreference voltage changes, there changes also the voltage at the base oftransistor 1, the voltage at the emitter of transistor 1, and thevoltage drop across the resistor 10. Because of the change in thevoltage drop across the resistor 10, the amplitude of the current pulsei is regulated.

The circuit is characterized by a small power consumption, because thevalue of the resistor is small in comparison to that of the loadresistor 5, and because a relatively low operating voltage is requiredin view of the small current demands of the circuit. The power consumed,which is the product of the current and the operating voltage, istherefore also small. Moreover, the circuit has the further advantagethat it reduces changes in the current caused by changes in the value ofthe load resistor 5. Finally, the circuit is simple and inexpensive,because the transistor 1 plays a double role: it turns on and off thecurrent through the load resistor 5, and it enables a controllablevariation of the voltage across the resistor 10, thereby enablingregulation of the current.

If it is desired that the amplitude of the current pulse i should beindependent of the temperature, the reference voltage between theterminal 7 andthe junction 8 is held constant.

The changes in the resistances of the load resistor 5 and of theemitter-collector path of transistor 1, caused by temperature changesand tolerances, are regulated by changing the voltage across theresistor 10. For example, if the value of the load resistor 5 becomessmaller, the voltage at the collector of transistor 1 is smaller andwith a constant emitter voltage, the collector-emitter voltage islarger, so that the amplitude of the current pulse i remains constant.The diode 6 regulates changes in the base-emitter voltage of transistor1, caused by temperature changes. This diode is connected so that itconducts. The effect of change in tem perature on the voltage dropacross the diode and across the base-emitter path of transistor 1 is thesame. If the voltage drop across the diode 6 increases, the voltage dropacross the base-emitter path likewise increases, wherebytemperature-caused changes of the emitter voltage of transistor 1 areregulated.

If the amplitude of the current pulses is to be independent oftemperature but dependent upon some other factor, there is providedbetween the terminal 7 and the junction 8 a reference voltage thatchanges in dependence on this other factor. Temperature changes are ofno consequence, because, as previously explained, they are compensatedby variations in the voltage drop across the resistor 10.

If the amplitude of the current pulse i is to be made dependent ontemperature, the aforesaid reference voltage is also made dependent onthe temperature.

With reference to FIG. 2, there is shown a circuit for regulating theamplitude of the current pulse i in dependence on the temperature. Thereference voltage must also be temperature-dependent. Atemperaturedependent resistance, such as the diode 12, connected betweenthe terminal 7 and the junction 8, provides the desired referencevoltage. At the same time, this component makes variations of i 2percent in the operating voltage ineffective.

The diode 6 is replaced by a second transistor 3, because thetemperature-dependent base-emitter voltage characteristics of the twotransistors l and 3 can be more accurately matched than can the changein voltage drop of a diode 6 to the change in the base-emitter voltageof transistor 1. The base electrode of transistor 3 is connected to thebase of transistor 1 whereas the emitter electrode of transistor 3 isconnected to the circuit junction 8. The transistors 1 and 3 areadvantageously of the same type with the same temperature dependency,exposed to the same temperature conditions, as by mounting them in thesame housing. The resistor 1 1 drains off the current that flows throughthe base-emitter path of transistor 1 when shutting off. Since theoperating voltage at the terminal 7 is more positive (+5 volts) than theground potential (0 volts), the transistors 1 and 3 are PNP types andthe transistor 2 is of NPN types. In accordance with the invention, theterminal 7 can be made negative with respect to ground, in which casethe transistors 1 and 3 are NPN types and the transistor 2 is a PNPtype.

The circuit shown in FIG. 2 is suitable as a current driver foroperating a matrix store. A circuit of this kind can send, for example,inhibit current pulses through the inhibit leads of matrix memories. Ifa current driver of this kind is to be used in the temperature range offrom 55C. to approximately C., the circuit is advantageously so designedthat the current pulse i through the load resistor 5 (the inhibit leadof the memory) flows in accordance with the curve K1, shown in FIG. 3.The temperature is plotted along the abscissa, and the current i isplotted along the ordinate. At 55C., the current i through the loadresistor 5 should be 450 milliamperes, and at +125 C., the currentshould be 350 milliamperes, corresponding to a change in current of lmilliampere /C.

The circuit enables the successive connection of a series of loadresistors, the values of which are not exactly equal.

With reference to FIG. 4, the temperature t is plotted along theabscissa, and the voltage U is plotted along the ordinate. Assuming thatthe current i is to follow the curve K1, shown in FIG. 2, the voltageacross the load resistor 5 must follow the curve K2. The curve K3 showsthe variation in voltage across the emitter-collector path oftransistor 1. The curve K4 shows the variation in the voltage betweenthe emitter of transistor 1 and ground, if the current through the loadresistor 5 is to follow the curve K1. The worst case is taken intoaccount in the curves K1 through K4. The curve K5 shows the voltage atthe terminal 7 with respect to ground.

The curve K6 is the difference between the curve K5 and K4. Curve K6thus shows the voltage across the resistor 10 required to obtain thedesired current i. The voltage corresponding to the curve K6 is obtainedby the diode 12, which produces the reference voltage at the junction 8.This reference voltage causes the desired current i throughout theentire temperature range.

In accordance with the invention, the reference voltage can belinearly'dependent on the operating voltage.

In will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofcircuits differing from the types described above.

While the invention has been illustrated and described as embodied incircuits for regulating the current, it is not intended to be limited tothe details shown, since various modifications and circuit changes maybe made without departing in any way from the spirit of the presentinvention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent is:

1. A circuit for regulating the amplitude of control pulses, comprisingin combination current path means for control pulses including a load,resistance means, a first transistor having a base and acollector-emitter path connected in series with said load and saidresistance means, said first transistor having predeterminedtemperature-dependent base-emitter voltage characteristics, and terminalmeans for connection with a source of operating voltage; controlledswitch means connected with said base of said first transistor and witha point of reference potential; a circuit junction; a second transistorcomprising base and emitter electrodes defining a junction havingtemperature-dependent voltage characteristics at least approximatingsaid predetermined characteristics, one of said electrodes beingconnected with the base of said first transistor, the other of saidelectrodes being connected with said circuit junction; and referencevoltage means connected between said terminal means and said circuitjunction.

2. A circuit as defined in claim 1, wherein said controlled switch meanscomprise an additional transistor having a collector-emitter pathconnected with said base of said first transistor and providing a pathfor the base current of said first transistor.

3. A circuit as defined in claim 1, wherein said first and secondtransistors are of the same conductivity type.

4. A circuit as defined in claim 1, wherein said one of said electrodesis said base electrode and wherein the other of said electrodes is saidemitter electrode.

5. A circuit as defined in claim 1, wherein said second transistorcomprises a collector electrode shortcircuited to said base electrode.

6. A circuit as defined in claim 1; and further including a resistorconnected between said terminal means and said base of said firsttransistor.

7. A circuit a defined in claim 1, wherein said load has a predeterminedresistance and said resistance means has a resistance less than saidpredetermined resistance.

8. The circuit as defined in claim 1, said reference voltage meansincluding temperature dependent resistance means connecting saidterminal means to said circuit junction.

9. The circuit as defined in claim 8, wherein said temperature dependentresistance means is a diode.

10. A circuit as defined in claim 1; and further comprising a source ofoperating voltage connected with said terminal means. v

11. The circuit as defined in claim 10, wherein said reference voltagemeans is linearly dependent on said operating voltage.

12. The circuit as defined in claim 10, wherein said reference voltagemeans is temperature dependent.

13. A circuit as defined in claim 1; and further said reference voltagemeans comprising fixed-potential means for providing a fixed potential,and wherein said controlled switch means is connected between said baseof said first transistor and said fixed-potential means.

14. The circuit as defined in claim 13, wherein said fixed potential isground.

1. A circuit for regulating the amplitude of control pulses, comprisingin combination current path means for control pulses including a load,resistance means, a first transistor having a base and acollector-emitter path connected in series with said load and saidresistance means, said first transistor having predeterminedtemperature-dependent base-emitter voltage characteristics, and terminalmeans for connection with a source of operating voltage; controlledswitch means connected with said base of said first transistor and witha point of reference potential; a circuit junction; a second transistorcomprising base and emitter electrodes defining a junction havingtemperature-dependent voltage characteristics at least approximatingsaid predetermined characteristics, one of said electrodes beingconnected with the base of said first transistor, the other of saidelectrodes being connected with said circuit junction; and referencevoltage means connected between said terminal means and said circuitjunction.
 2. A circuit as defined in claim 1, wherein said controlledswitch means comprise an additional transistor having a collectoremitterpath connected with said base of said first transistor and providing apath for the base current of said first transistor.
 3. A circuit asdefined in claim 1, wherein said first and second transistors are of thesame conductivity type.
 4. A circuit as defined in claim 1, wherein saidone of said electrodes is said base electrode and wherein the other ofsaid electrodes is said emitter electrode.
 5. A circuit as defined inclaim 1, wherein said second transistor comprises a collector electrodeshort-circuited to said base electrode.
 6. A circuit as defined in claim1; and further including a resistor connected between said terminalmeans and said base of said first transistor.
 7. A circuit a defined inclaim 1, wherein said load has a predetermined resistance and saidresistance means has a resistance less than said predeterminedresistance.
 8. The circuit as defined in claim 1, said reference voltagemeans including temperature dependent resistance means connecting saidterminal means to said circuit junction.
 9. The circuit as defined inclaim 8, wherein said temperature dependent resistance means is a diode.10. A circuit as defined in claim 1; and further comprising a source ofoperating voltage connected with said terminal means.
 11. The circuit asdefined in claim 10, wherein said reference voltage means is linearlydependent on said operating voltage.
 12. The circuit as defined in claim10, wherein said reference voltage means is temperature dependent.
 13. Acircuit as defined in claim 1; and further said reference voltage meanscomprising fixed-potential means for providing a fixed potential, andwherein said controlled switch means is connected between said base ofsaid first transistor and said fixed-potential means.
 14. The circuit asdefined in claim 13, wherein said fixed potential is ground.